Humans use a wide variety of tools where the orientation of the tool relative to the user is critical to safe and effective operation. For example, the orientation of a bow or gun relative to a shooter will determine the accuracy and repeatability of a shot. Golfers spend a great deal of time positioning themselves relative to the golf ball and golf clubs in order to develop a consistent and repeatable golf swing. In board riding athletic activities, such as skiing, surfing, snowboarding, windsurfing, and the like, the posture and position of the rider relative to the board is critical. Free-hand power tools, such as drills, planners, routers and saws, operate best and safest when consistently positioned relative to the user's body.
For many tools, however, it is not possible to align the user's line of sight with an operating axis/plane of the tool. Rather, the operating axis/plane of the tool and the line of sight of the user need to converge at a particular location. For example, the operating axis of a pool cue is along the axis of the cue. The pool player does not sight along the operating axis of the pool cue. Rather, the pool player's line of sight and the operating axis of the pool cue converge, typically at the cue ball. In another example, the operating axis of a bow is co-linear with the arrow. Modern bows, however, do not permit the user to sight along the axis of the arrow. Consequently, the user must position his or her body in a fixed relationship with the bow, as a surrogate to sighting along the operating axis of the arrow.
Over time a user can develop the skill to make the tool an extension of his or her body so the operating axis/plane of the tool and the user's line of sight converge in the correct location. The current mechanisms for accelerating this learning process, however, are crude and inaccurate.
Using archery as an example, the alignment of a shot can vary dramatically depending on where the archer positions his or her head, or more particularly, his or her shooting eye relative to the bow. If the archer's eye position varies from shot to shot, so will the accuracy and direction of each respective shot, leading to inconsistent or unpredictable shooting. U.S. Pat. No. 5,850,700 proposes an eye alignment apparatus that assures that the archer's shooting eye is consistently positioned relative to the bow and the bow sight, which is hereby incorporated by reference.